Electrolytic apparatus



April 23, 1968 H. HENIG ELECTRQLYTIC APPARATUS 2 Sheets-Sheet 1 Filed Feb. 26, 1964 FIG. 2.

April 23, 1968 H. HENIG ELECTROLYTIC APPARATUS 2 Sheets-Sheet 2 Filed Feb. 26, 1964 O 2 9 2 4 f m WW n w 1 il a s x 4L W WQ n 1w V w W .A h A Q in I III; m o 4 a m M 5 I 1 United States Patent ELECTROLYTIC APPARATUS Hans Henig, Sulzbacherstrasse 31,

Nuremberg, Germany Filed Feb. 26, 1964, Ser. No. 347,613 Claims priority, application Germany, Mar. 27, 1963, H 47,383 2 Claims. (Cl. 204-213) This invention concerns improvements in or relating to electrolytic apparatus. It is already Wfill known that small metal or metallic parts such as bolts, screws, and so on, can be electroplated in bulk by a technique generally referred to as barrel plating, in which the load of small metal parts is placed within a tumbling barrel or drum which is rotated in the plating electrolyte. The electrolytic deposition of a plating upon the metal parts is then effected by creating an electrical potential field within the electrolyte which causes ions from the electrolyte to plate out upon the surface of the parts and form metallic coating layers thereon.

It is of course already well recognized that with apparatus of this type the amount of metal deposited from the electrolyte, and its distribution between the various individual metal parts which make up the load, are much influenced by the geometry of the electrical potential field created in the electrolyte, and the field in turn depends primarily upon the arrangement of the electrodes on the one hand and the nature and location of the load on the other hand.

To achieve a uniform electrolytic deposition throughout the load it is of course desirable to achieve a uniform current distribution, which however is a matter of some difficulty. In efiorts to achieve this desideratum it has been proposed to provide, apart from the usual anode and cathode, an additional electrode whose purpose is to influence the potential field and thus promote more even deposition. Thus where the small metal parts within the barrel are connected to the negative pole so as to constitute the cathode and a soluble anode is provided in the electrolyte outside the barrel, it has been suggested that an additional anode should be provided within the barrel, disposed above the load. Again, it has also been proposed to shape or position the external anode or anodes in such a manner as more completely to encircle the barrel.

While these proposals advantageously influence the current distribution, and the latter proposal in particular ensures uniform current density over the surface of the barrel, neither produces uniform deposition throughout the entire load, and indeed the electrolytic deposition takes place mainly in the surface layers of the load immediately adjacent the periphery of the barrel.

Careful investigation has in fact shown that the drop in electrical potential between each individual metallic part in the load and its neighbouring electrolyte falls off very rapidly from the surface layers of the load towards the centre of the load. Moreover, it has been observed that in practice the rotation of the barrel does not bring about a complete intermingling of the small parts making up the load. Thus, parts which are on the outside of the load at the beginning of the process tend in general to remain on the outside throughout it, and vice versa. As a consequence of both the non-uniform plating and the non-mixing of the load parts, the thickness of the plating electrolytically deposited on any individual metallic part tends to depend on its initial position relative to the load centre.

The purpose of the present invention is to secure a more uniform electrolytic deposition throughout the barrel load primarily by increasing the mean potential drop 3,379,631 Patented Apr. 23, 1968 between each individual part and the neighbouring electrolyte, and by rendering the electrical field within the load more homogeneous than has hitherto been possible.

According to the invention there is therefore provided an apparatus for electroplating small metal parts in bulk comprising a foraminous barrel adapted in operation to receive a load of small metal parts within its interior and upon rotation to immerse that load at least partially in the plating electrolyte, one or more first electrodes disposed within the barrel, separator(s) disposed about said first electrodes to prevent direct contact of the load therewith, one or more second electrodes so disposed within the barrel as directly to contact the load of metal parts, and one or more third electrodes disposed external of the barrel, said first and third electrodes being adapted for connection to one pole and said second electrodes being adapted for connection to the other pole of a direct current source.

Thus it will be seen that the load of small metallic parts, connected via the second electrode to one pole, usually the cathode, is penetrated with an electrode of opposite sign, thus the aforesaid first electrode which is separated from direct contact with the load, and in the usual case constitutes an anode. The conglomeration of small metallic parts thus has electrodes of opposite sign disposed therein, with one of which the load is in direct electrical contact and from the other of which it is separated by a perforated insulator or the like.

It appears probable that the positive electrode introduced into a cathodically connected load (or vice versa) has the effect of creating a potential field within the load which promotes a more uniform current pattern. Whether or not that theory is correct, it is an established fact that the use of the invention makes possible the production of very uniform platings on all parts of the load independent of their position within the barrel.

The first electrodes are preferably disposed substantially axially of the barrel, and most conveniently constitute a fixed tubular axis about which the barrel rotates. The load penetration of the first electrodes can be increased by the fitting to the tubular construction one or more radially extending disc-shaped extensions.

The separator will advantageously comprise a perforate sheath or sleeve of insulating material disposed about the first electrode, and preferably spaced radially and concentrically about a fixed tubular electrode. This perforated sheath is best mounted for rotation with the barrel about the fixed electrode in order to prevent jamming.

In the embodiment using disc-shaped extensions to the first electrode, these will of course also be sheathed.

The second electrodes are intended to make direct contact with the load and should therefore be so disposed within the barrel as to ensure that they contact the load even when the barrel is not fully charged. They should thus extend in the normal case nearly to the lowermost point, and they may most conveniently be introduced within the barrel via insulated connections carried along the axis of the barrel and then extending substantially radially therefrom. The preferred construction indeed involves the insulated leads for the second electrode passing through the fixed tubular first electrode and emerging therefrom through apertures in the tube and its surroundin g sheath.

FIGURE 1 is a part-sectional front elevation view of one embodiment of a barrel plating apparatus taken in a vertical plane passing through the rotational axis of the barrel;

FIGURE 2 is a sectional view through the embodiment shown in FIGURE 1, taken in a vertical plane normal to the rotational axis of the barrel;

FIGURE 3 is a view similar to that shown in FIGURE 1 of another embodiment of a barrel-plating apparatus in accordance with the invention; and

FIGURE 4 is a view similar to that shown in FIGURE 2 of the same embodiment as shown in FIGURE 3.

Referring now to FIGURES l and 2, in which, for convenience, the electrolyte and its container are not shown, the barrel-plating apparatus comprises a barrel, generally indicated 1, carried upon support arms, 2, 3 (see FIGURE 1) and immersed wholly or partially in an electrolyte (not shown) between soluble anodes 4, 5 which are detachably secured to bus-bars 6, 7. Within the barrel 1 there is a load of small metallic parts schematically indi cated at S, which, upon rotation of the barrel in the direction indicated by arrow 9, assumes a distribution within the barrel somewhat as indicated.

The barrel 1 comprises hexagonal end plates and 11 between which extend perforate synthetic resin or like non-conductive material walls 12 defining the outer periphery of the barrel. The wall on one face of the barrel periphery takes the form of a detachable cover 13 through which the load can be charged into barrel 1, or removed therefrom.

The edge of end plate 10 is provided with gear teeth 14 which can be driven (by means not shown) to rotate the barrel 1 about the tubular axis 15, carried by support arms 2 and 3, upon which the barrel is rotatably mounted. The tubular axis 15 is connected directly to the positive pole of a direct current source (not shown), which is conveniently a rectifier. The tubular axis 15 thus serves as an anode, and is surrounded by a perforate synthetic resin or like material sheath 16 whose ends are fixedly secured to end plates 10 and 11 and rotate therewith about axis 15, preventing the load within barrel 1 from directly contacting the anode 15.

Within the barrel 1, thus between its outer wall 12 and the sheath 16, and in direct contact with the load, there are arranged cathodes 17, 18 which are connected via insu lated leads 19, 2%] with the negative pole of the rectifier or other current source. These insulated leads 19 and 29 respectively both pass through apertures in the tubular anode 15 and overlying insulating tube sections 21 and 22.

Referring now to FIGURES 3 and 4, it will be noted that this embodiment is, in general, similar to that shown in FIGURES 1 and 2 above, and similar parts are indicated with the same reference numerals. The embodiment of FIGURES 3 and 4, however, incorporates a disc-shaped anode extension 23 disposed centrally of the tubular anode 15, and extending radially nearly to the periphery of the barrel 1. This extension 23 is separated from direct contact with the barrel load by partitions 24 and 25 disposed to each side of it, formed of perforate synthetic resin or like insulating material similar to that used for the outer walls and the sheath 16, between which of course these partition walls extend, dividing the interior of the barrel -1 into two compartments into which the cathodes 17 and 18 respectively protrude.

I claim:

1. Electrolytic apparatus comprising a container for plating electrolyte, a tubular anode fixedly supported in said container, a drum having end walls and a perforate non-conducting peripheral Wall mounted to rotate on said tubular anode, said peripheral wall being spaced from said tubular anode, a stationary perforate non-conducting sleeve closely surrounding said tubular anode, at least one stationary soluble electrode located in said container outside of said drum, at least one stationary cathode extending into said tubular anode and through openings in the wall of said tubular anode and in said perforate sleeve into the space between said sleeve and said peripheral wall, and being insulated from said tubular anode, and electrical connections to all of said electrodes.

2. Electrolytic apparatus as defined in claim 1, in which a conductive disc extends outwardly from said tubular anode intermediate the ends thereof and perforate non-conducting discs extend from said perforate sleeve to said perforate peripheral wall on each side of and adjacent to said conductive disc.

References Cited UNITED STATES PATENTS 617,512 1/1399 Porter 204-213 1,509,534 9/1924 Todd 204 213 2,035,633 3/1936 Bogle 204-213 3,133,177 5/1965 DeSante etal 204-213 FOREIGN PATENTS 2,159 1900 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

W. VAN SISE, Assistant Examiner. 

1. ELECTROLYTIC APPARATUS COMPRISING A CONTAINER FOR PLATING ELECTROLYTE, A TUBULAR ANODE FIXEDLY SUPPORTED IN SAID CONTAINER, A DRUM HAVING END WALLS AND A PERFORATE NON-CONDUCTING PERIPHERAL WALL MOUNTED TO ROTATE ON SAID TUBULAR ANODE, SAID PERIPHERAL WALL BEING SPACED FROM SAID TUBULAR ANODE, A STATIONARY PERFORATE NON-CONDUCTING SLEEVE CLOSELY SURROUNDING SAID TUBULAR ANODE, AT LEAST ONE STATIONARY SOLUBLE ELECTRODE LOCATED IN SAID CONTAINER OUTSIDE OF SAID DRUM, AT LEAST ONE STATIONARY CATHODE EXTENDING INTO SAID TUBULAR ANODE AND THROUGH OPENNGS IN THE WALL OF SAID TUBULAR ANODE AND IN SAID PERFORATE SLEEVE INTO THE SPACE BETWEEN SAID SLEEVE AND SAID PERIPHERAL WALL, AND BEING INSULATED FROM SAID TUBULAR ANODE, AND ELECTRICAL CONNECTIONS TO ALL OF SAID ELECTRODES. 